1. Field of the Invention
The present invention relates to an ink jet recording apparatus.
2. Related Background Art
As recording apparatuses for expressing print information such as a character or an image by printing a group of dots, dot-matrix printers are known. Of these printers, an ink jet printer for ejecting ink jet droplets onto a recording medium has become increasingly popular due to its simple mechanism, low-noise or easy color expression feature, or the like.
FIG. 16 shows a print pattern. A print head 100 has an array of a plurality of nozzles NL to NH as ink ejection orifices. Ink droplets are ejected from these nozzles and land on a recording sheet. The print head 100 is moved in the X-direction in FIG. 16 while repeating the ejection operation (FIG. 16 also shows a landing state at that time). Upon completion of a print operation by a predetermined width, the recording sheet is fed, in turn, by a predetermined amount in the Y-direction in FIG. 16. In this manner, the recording operation progresses. FIG. 17 is a timing chart of a head driving operation for arbitrary dots N1 to N4 shown in FIG. 16. In this case, a 4-dot split driving method is employed, and is executed in the order of N1, N3, N2, and N4. The driving timings of the adjacent nozzles have an interval t1, as shown in FIG. 17. The interval t1 is a minimum value determined by a timing on a head driver or software, and it is impossible to drive the nozzles at a time interval shorter than t1. The print head 100 is scanned in the Y-direction while performing ejection operations of the nozzles at these timings, thus printing lines L1, L2, . . . .
FIG. 18 shows a block driving method different from an N-dot split driving method. In this method, the above-mentioned nozzles N1 to N4 are simultaneously driven to perform a print operation. Blocks are respectively represented by B1 to B8 (in the case of a 32-nozzle head), and a minimum driving interval between the adjacent blocks is represented by t2. Time interval t2 is a value limited by the hardware or software configuration of the recording apparatus, and it is impossible to drive the blocks at a time interval shorter than t2.
The nozzle portions as ink ejection orifices suffer from a variation in ejection direction due to manufacturing errors. The variation in ejection direction appears as periodic nonuniformity in a print result since it is reproduced at a line feed pitch of the recording apparatus. When an ink is printed at a speed higher than an ink penetration speed in a recording medium, the printed ink overflows, resulting in blurring or color mixing.
As a method of preventing this phenomenon, a multi-pass print method based on a thinning operation is known. In the case of a 2-pass print mode as an example of the multi-pass print method, some dots, e.g., dots from odd-numbered nozzles are printed in the first-pass carriage scan operation, a line feed operation is performed by an amount 1/2 a normal amount, and dots from even-numbered nozzles are printed in the second-pass carriage scan operation.
However, according to the multi-pass print method, since the print operations are intermittently performed, the print time is prolonged considerably, and the throughput of the printer is decreased.